Embodiments of the present disclosure relate to a semiconductor device, and more particularly to a semiconductor device including a reservoir capacitor.
Generally, a semiconductor device such as a DRAM includes a large number of small elements and generates an internal voltage to operate these elements. For example, various power sources are used to operate capacitors in a cell region and semiconductor elements in other regions that include a peripheral circuit region. When power sources supply voltages to the semiconductor elements, the supplied voltages may have unstable levels because of noise included therein. A reservoir capacitor may be used to reduce such noise and stabilize the supply of a power voltage and/or a ground voltage.
Typically, a reservoir capacitor is disposed in a peripheral circuit region of a semiconductor device and includes a plurality of Metal-Oxide-Semiconductor (MOS) transistors, each of which includes a gate, a source, and a drain. A source and a drain of a MOS transistor are electrically coupled to each other and form one end of a MOS capacitor so that the MOS transistor acts as the MOS capacitor.
A MOS capacitor includes a gate oxide film that has superior inner pressure characteristics when a voltage is applied to both ends of the MOS capacitor. Assuming that there is sufficient space for forming capacitors in a peripheral circuit region, MOS capacitors can be formed in the peripheral circuit region when MOS transistors are formed in a cell region. That is, the MOS capacitors disposed in the peripheral circuit region and the MOS transistors disposed in the cell region can be formed in the same process. Thus, a fabrication process of a semiconductor device can be simplified.
However, as the integration degree of a semiconductor device increases, the integration degree of the peripheral circuit region also increases. As a result, the size of a region in which a reservoir capacitor including a plurality of MOS capacitors can be formed is reduced. While a MOS capacitor has superior inner pressure characteristics for a voltage applied to both ends thereof, since a MOS capacitor has low electrostatic capacitance per unit area, it is difficult to use MOS capacitors as a reservoir capacitor in a highly-integrated semiconductor device.